1. Field of Invention
This invention relates in general to satellite navigation systems and, in particular, to wireless communication devices utilizing a Global Positioning System (“GPS”) receiver.
2. Related Art
The use of telecommunication devices in present day society has grown at an enormous rate. Currently, the demand for portable telecommunication devices such as cellular telephones, Wi-Fi® and Bluetooth*) enabled portable devices, Personal Communication Service (“PCS”) devices, Global Positioning System (“GPS”) enabled portable devices, etc., is growing in popularity every day. As the demand increases for portable telecommunication devices with varying communication characteristics, manufactures are seeing a need to combine and integrate many of these devices. As an example, there is a need to integrate cellular telephones (i.e., “cellphones”) with GPS receivers in order to allow a cellphone to determine its position for both personal and emergency use.
In FIG. 1, a block diagram of an example of a known implementation of a wireless device 100, such as a cellphone, communicating with a communication network 102 and GPS satellites 104, is shown. The wireless device 100 may be, for example, a cellphone and it may include a wireless transceiver 106, a GPS section 108 (where the GPS section 108 may be a GPS receiver or GPS tracker), and battery 110. In operation, the wireless transceiver 106 may be in signal communication with communication network 102 via wireless signal path 112 and basestation 114 and the GPS receiver 108 may be in signal communication with the GPS satellites 104 via wireless signal path 116.
The need for integrating cellphones with GPS receivers is a result of the U.S. Congress though the FCC mandating that cellular service providers report the position of a cellular handset that has dialed 911 to an emergency call center. The required accuracy is 100 meters for 67 percent of emergency calls, 300 meters for 95 percent of emergency calls for network-based solutions, and 50 meters for 67 percent of calls and 150 meters for 95 percent of calls for handset-based solutions. To comply with this mandate, many service providers require that handsets used on their system contain embedded GPS receivers. The FCC has extended the requirement for “E911” position reporting to VoIP service providers and to satellite telephone service provides. Handset standby time is very important to consumers, and hence to service providers.
Unfortunately, location based services require near instant position fixes that require significant power; however, these fixes can be refined over the next several seconds for improved accuracy. In general, embedded GPS receivers can provide near instant position fixes provided they have minimal time, frequency, and to some extent, position uncertainties predetermined. Unfortunately, at present, GPS receivers do no have the ability to operate continuously without draining the power source (such as a battery).
Known approaches to this problem have included utilizing power cycling modes that have stronger signal requirements for the same or greater energy expenditure of the battery. These approaches include making fixed (i.e., blind) uncertainty assumptions about the real-time clock (“RTC”) when using the RTC to store time. Unfortunately, these cycling mode approaches do not use stationary assumptions and/or indoor assumptions to determine how measurements made within the cycle are used or interpreted; instead, these approaches generally return the GPS receiver to full power operation. These approaches do not take advantage of the Temperature Controlled Crystal Oscillator (“TCXO”) stability in the absence of GPS measurements. Additionally, these approaches do not infer temperature or temperature rate from relative RTC and TXCO frequency and they do not operate against an energy constraint because they only operate against an update rate.
Aiding information can be provided over communications networks, but this requires the ability to receive aiding over a communication network. Thus, it is desirable for an embedded GPS receiver to maintain accurate estimates of time, frequency, and position. These accurate estimates would allow the embedded GPS receiver to acquire signals at lower levels.
Therefore, there is a need for system and method capable of minimizing the power source drain of the embedded GPS receiver when fixing the position of a wireless device.